Orthodontics involves purposefully moving teeth towards a certain predefined pattern so that the tooth row has an esthetically pleasing look. The condition of crowded or crooked teeth is called malocclusion. Although ancient attempts to correct malocclusion date back to 1000 BC, modern orthodontics began slightly more than a century ago [Proffit et al., (1993) Mosby Year Book: St. Louis. pp. 266-288].
In late 1800s, Edward Angle placed metal bands on the teeth and used continuous wires that fit into the slots of the bands. Elastics were used to apply forces with a result of aligning the teeth along the xe2x80x9ctrackxe2x80x9d of the wire. The forces applied by Angle were static and continuous, meaning that once the forces have been generated by elastics, the forces are continuously present unless and until they decayed to nil.
Since Angle""s practice, orthodontists have used static forces to induce orthodontic tooth movement. Contemporary orthodontic treatment takes an average of two years to complete in one patient, involving multiple visits and repeated activations; i.e., reasserting the force on the teeth. No one has attempted to determine whether cyclic forces; i.e., forces with rapidly varying magnitude over time, induce more rapid tooth movement than the presently used continuous forces.
Orthodontics involves the use of mechanical forces to move teeth within the jaw bone and therefore, relies on force-induced bone remodeling. A force is a physical quantity and has several essential properties such as the magnitude, direction, point of application and frequency. All these properties of orthodontic forces have been subjects of scientific research and considered in clinical practice of orthodontics with the exception of force frequency. Exclusive use of continuously applied static forces in orthodontics and the resulting lack of consideration of force frequency contradict the overall scientific consensus-based evidence obtained from orthopedic studies of long bones that cyclic forces induce more effective bone remodeling than static forces of matching magnitude.
The main advantage of the current orthodontic technology of using continuously applied static forces to move the teeth towards predetermined positions to achieve esthetically pleasing look is its predictable, albeit slow, outcome, inducing controlled tooth movement towards predetermined position when treatment is carried out by a competent orthodontist. The principal shortcoming of the current technology is its requirement of excessively long treatment duration: approximately two years on average. The essential reason for this excessively long treatment duration is due to a lack of efficiency resulting from the present use of continuously applied static forces.
More specifically, except as described hereinafter, only continuously applied static forces have been studied and/or used in previous studies and clinical practice in orthodontics. First, about 36 percent of the US population receive orthodontic treatments [Brunelle et al., (1996) J. Dent. Res., 75(Spec Iss):706-713]. Continuously applied static forces are used on a daily basis for orthodontic tooth movement in these patients. Second, in addition to day-to-day practice of application of continuously applied static forces in clinical orthodontics, orthodontic tooth movement has been simulated in animal models with elastics and coil springs [Reitan (1951) Acta Odont. Scand. Suppl., 6:1-240; Storey et al., (1952) Aust. J. Dent., 56:11-18; Pygh et al., (1982) In Berkivitz et al. (Eds) The Periodontal Ligament in Health and Disease, Pergamon Press, Oxford, England, pp. 269-290; Jager et al., (1993) Histochemistry, 100:161-166; Ashizawa et al., (1998) Arch Oral Biol., 43(6):473-484; Gu et al., (1999 Angle Orthod. 69(6):515-522; Melsen (1999) Angle Orthod., 69(2):151-158; Terai et al., (1999) J. Bone Miner. Res., 14(6): 839-849; Tsay et al., (1999) Am. J. Orthod. Dentofacial Orthop., 115(3):323-330; and Verna (1999) Bone, 24(4):371-379]. Without exception, continuously applied static forces have been used in all these studies.
Although there have been previous attempts to use xe2x80x9cintermittent forcesxe2x80x9d, the nature of the intermittent forces were static forces applied intermittently over time, for instance, two hours on and two hours off [Reitan (1951) Acta Odont. Scand. Suppl., 6:1-240; van Leeuwen et al., (1999) Eur. J. Oral Sci., 107(6):468-474] instead of the hereinafter described cyclic forces that rapidly change magnitude over short time, e.g. several cycles per second. The current technology of continuous, constant and static forces, such as those used in orthodontics, lacks either frequency modulation or change in force magnitude over time.
In addition to a lack of consideration of force frequency in both research studies and clinical practice of orthodontics as described above, both the threshold force and the duration of force application, which are two additional essential properties of a force, are not clearly understood in the field of orthodontics. First, a minimum of 6 hours has been thought to be the threshold below which orthodontic tooth movement does not occur [Proffit et al., (1993) Mosby Year Book: St. Louis. pp. 266-288]. However, this projected minimum threshold of 6 hours per day by Proffit et al. is largely theoretical, as stated in the caption of FIGS. 9-12 on page 275 of that work.
Although empirical clinical experience appears to support the notion that orthodontic forces must be applied beyond certain daily duration in order to induce tooth movement, the precise minimum daily duration is unclear. What appears of more significance than daily minimum duration is the overall duration of orthodontic treatment in association with current technology. The use of cyclic forces in orthodontic tooth movement described hereinafter can significantly shorten the present average two-year duration of orthodontic tooth movement.
Although there are more data on the threshold force magnitude required for tooth movement, the precise threshold is yet to be determined. In general a few hundred grams of force have been implicated to be the threshold for tooth movement. However, there remain projections as xe2x80x9ctheoretically, there is no doubt that light continuous forces produce the most efficient tooth movementxe2x80x9d [Proffit et al., (1993) Mosby Year Book: St. Louis. pp. 266-288]. Although it has been shown that proliferation of periodontal ligament cells is greater in response to continuous forces than to intermittent forces of the same magnitude [Reitan (1951) Acta Odont. Scand. Suppl., 6:1-240], the previously investigated intermittent forces were static forces applied intermittently over time [Reitan (1951) Acta Odont. Scand. Suppl., 6:1-240; van Leeuwen et al., (1999) Eur. J. Oral Sci., 107(6):468-474] instead of the presently proposed cyclic forces that rapidly change magnitude within time units of seconds.
Contemporary orthodontists not only use braces to align the teeth, they also use orthopedic appliances such as headgear and facemask to change the shape of facial bones so that the overall facial shape is esthetically pleasant. The present technology (described hereinafter), in addition to providing a mechanism for rapidly aligning the teeth, also provides pathways by which the shape of facial bones can be rapidly changed, although the precise characteristics of the forces responsible for the two approaches are different. The present invention that is described hereinafter provides for the remodeling of craniofacial bones and treatment of malocclusion through the use of cyclic force application to the region to be remodeled.
In accordance with the present invention, cyclic forces are used to expedite the remodeling of craniofacial bones to correct dentofacial deformities and expedite the remodeling of alveolar bone to treat malocclusion. One aspect of the invention contemplates a method for inducing a predetermined amount of osteogenesis in the craniofacial bones of a mammal in need thereof. That method comprises the steps of (a) applying cyclic forces to a craniofacial suture region of the mammal in which osteogenesis is desired with a peak magnitude of up to about 10 Newtons, and preferably about 0.1 to about 5 Newtons, and frequencies of up to about 40 Hz, and preferably about 0.1 to about 8 Hz, for a predetermined period of time. That application is (b) repeated a plurality of times until a predetermined amount of osteogenesis is obtained.
Another aspect of the invention contemplates a method for realigning one or more of the teeth of a mammal in need thereof. That method comprises the steps of (a) applying cyclic forces to at least one tooth of the mammal in which tooth realignment is desired with a peak magnitude of about 10 Newtons, and preferably about 0.1 to about 5 Newtons, and a frequency of up to about 40 Hz, and preferably about 0.1 to about 8 Hz, in a direction of the desired realignment for a predetermined period of time. That application is (b) repeated a plurality of times until a predetermined amount of tooth realignment is obtained.
A particular apparatus for treating malocclusion is another contemplated aspect of this invention. This apparatus comprises a band and bracket of generally inelastic material that are affixable to one or more teeth. The band has first and second ends that are joined at a centralized hub. A power source connected to an actuator assembly is provided to generate cyclic mechanical forces with a peak magnitude of up to about 10 Newtons, and preferably about 0.1 to about 5 Newtons, and a frequency of up to about 40 Hz, and preferably about 0.1 to about 8 Hz in a direction of the desired realignment desired at the centralized hub and thereby to the band. The power source and actuator are controlled by a microprocessor that can direct the duration of the application of the force as well as the repeated application of the cyclic mechanical force.
A method for treating malocclusion to realign teeth in a mammal in need thereof is another contemplated aspect of this invention. This method comprises the steps of providing a band of generally inelastic material that is affixed to one or more teeth of the mammal to be treated. The ends of the band are joined at a centralized hub. A power source connected to an actuator assembly is used to apply cyclic mechanical forces with a peak magnitude of up to about 10 Newtons, and preferably about 0.1 to about 5 Newtons, and a frequency of up to about 40 Hz, and preferably about 0.1 to about 8 Hz, in a direction of the desired realignment desired at the centralized hub and thereby to the band, the cyclic forces being applied for a predetermined time period. The power source and actuator are controlled by a microprocessor that can direct the duration of the force application and the repeated application of the cyclic mechanical force. The cyclic mechanical forces are applied a plurality of times until the teeth are realigned and malocclusion is treated.
The present invention has several benefits and advantages. One benefit of the invention is its use to substantially markedly shorten the duration of orthodontic treatment as compared to the current technology.
An advantage of the invention is that craniofacial bone restructuring can be accomplished more rapidly than has been possible using previously known techniques.
Another benefit of the invention is an apparatus that can realign maloccluded teeth.
Still further benefits and advantages will be apparent to the skilled worker from the disclosure that follows.